does the floor really need to be level before laying tiles?

Marbles in my case, what if the floor is not perfectly level, but it does not bouncy, can I still lay marble tiles on it? with or without backer board? If someone said no, I would wonder why? I saw interlock outside not being level...

I don't want to spend expensive leveling compound to level my washroom before laying Marble Tiles.... I wouldn't mind too much putting on some wonder board before laying tiles, but wonder if I can even get away from doing that considering there is minimum or no water at that washroom in the basement...

Any advice are appreciated...

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does the floor really need to be level before laying tiles?

Ok...first of all, I think I gathered that you are tiling your washroom which is in a basement. I assume that the floor is concrete, no?
If so, you will not be using backerboard on top of the concrete...If you wanted to do a decoupling type membrane you could use Ditra (made by Shulter Systems) that would be ideal for a concrete basement floor...it is a membrane that you thinset to the floor and then thinset on the membrane and then tile.
If you are not using Ditra you would set the tile on the concrete.

does the floor really need to be level before laying tiles?

That is strange...How is it secured to the floor? This is important because if it is clicked and locked into place only, it is "floating" and that may affect movement of the floor and therefore cause tile and grout cracking.I dont know what the protocol is for this kind of floor and installing tile other then what is stated below...you would need to permently attach the subfloor to the concrete to prevent movement.
Here is the information from the Dricore site regarding ceramic tile installation if it is indeed like this product:

"Ceramic Tile: DRIcore is designed to act as a floating subfloor. It is not recommended that Ceramic tile be directly attached to DRIcore as the movement of the floating subfloor will cause tile and grout lines to crack. There have been successful installations that are not covered under a warranty using ¼” underlayment or ½” cement board suitable for ceramic tile installations. In the case of a ceramic installation, prepare concrete floor by applying liquid concrete leveling compound to the concrete floor surface to level to eliminate concrete floor height variances. It is acceptable to fasten each panel with four, flat head and countersunk, concrete fasteners per panel to the permanent concrete floor to prevent movement or shifting of the finished ceramic tile floor. If you are concerned about moisture penetration through fastening points, a dab of silicone in the fastener openings will help seal these holes. DRIcore panels must lay perfectly flat without bounce or deflection. Follow the underlayment manufacturer’s installation guidelines for fastening to a subfloor, using fasteners that will not penetrate the moisture barrier underneath DRIcore panels.

Please note that we also do not recommend gluing underlayments or other wood flooring materials to DRIcore. As a general practice, it is best to minimize the amount of fastening through DRIcore panels to maintain the integrity of the moisture barrier."

OR are there sleepers or some other kind of floor joist there that the wood is secured to then, depending on its thickness and strength, would be ok for cementboard and tile.
As for the slope, if you are installing large format tiles, you may get excessive lippage on the tile...

does the floor really need to be level before laying tiles?

I tapcon the plywood onto the concrete, it is concrete, a thick plastic sheet with studs... then plywood... I put enough tapcon so that the plywood is quite strong, no bounce...

I used 1 ft by 1 ft marble tile, would it get "excessive lippage " what is "excessive lippage " means actually... I did look at the dictionary before asking, but couldn't figure out...

I did read the Dricore article above before... doesn't say much to me... I am not buying their product and their warantee to me is meaningless... but I know you means that means they are not recommending doing so...

I kind of knowing this too late, after doing it and now I kind of don't want to pull them out either...as may be it give some insulation effect with the plastic and plywood...etc...

does the floor really need to be level before laying tiles?

Are you saying that the floor is not level or has dips in it? If the floor is flat but not perfectly level and you don't mind you can put the tile down with out a problem. If the floor has dips or sags in it, that is where you will get the excessive lippage. Which means one tile is higher or lower than the next and there will be a lip sticking up.

does the floor really need to be level before laying tiles?

Kuip,

I wasnt showing you the Dricore info to let you know about the warentee information, I was trying to show you that if the subfloor was like dricore in that it is "click and locked" into place and not secured to something, that they would need to be screwed into concrete...the bold type was in the text origianlly.......but from what I gather you are saying that there are joists there and that the plywood is secured to the joists....this is not like dricore...dricore is "floating" in that it is not actually attached to the concrete below...
Bounce is not the issue...the issue is movement in the subfloor compromising the tile installation.
SO from what you describe, it should be OK to thinset and screw backerboard into the plywood and then install tile.
In any case, the subfloor needs to be secured to the concrete in some way to prevent movement...
Excessive lippage just means that if the floor is unlevel in an area or has dips as stated above, the edge of the tiles may "stick up" when layed next to eachother...

does the floor really need to be level before laying tiles?

Dont secure the backerboard with long screws into the concrete.
Comb a layer of thinset onto the plywood, embed the backerboard in the thinset and screw it in with "Rock-On" screws...that is a particular brand but they make others...just to be sure to use one that is approved for backerboard they work best...dont use drywall screws.
I like the 1/4" Hardibacker because it is light and has a screw grid so you can verify that you have put enough screws in it...You dont need to use 1/2"....the backerboard purpose is not to add strength to the floor it is simply to provide a good bond for the thinset.

does the floor really need to be level before laying tiles?

Quote:

Originally Posted by dougrus

Dont secure the backerboard with long screws into the concrete.
Comb a layer of thinset onto the plywood, embed the backerboard in the thinset and screw it in with "Rock-On" screws...that is a particular brand but they make others...just to be sure to use one that is approved for backerboard they work best...dont use drywall screws.
I like the 1/4" Hardibacker because it is light and has a screw grid so you can verify that you have put enough screws in it...You dont need to use 1/2"....the backerboard purpose is not to add strength to the floor it is simply to provide a good bond for the thinset.